Filamentous hemagglutinin is a large molecular weight protein expressed by virulent strains of Bordetella pertussis that is a bacterial adhesin. Our studies are focused on the detailed molecular analysis of this protein using electron microscopic techniques together with biochemical and immunological strategies. The electron microscopic studies are being done in collaboration with Dr. Steven~s laboratory at NIDDK. The current data suggests that FHA forms an unique hairpin-like structure and future studies will address whether this conformation effects the adhesive functions of FHA. Additional work in collaboration with Dr. Mink at the St. Louis University will analyze the human immune response to FHA following disease and vaccination. These studies will be based on earlier work done in our laboratory which established the presence of two major immunodominant regions on the FHA molecule. Fusion proteins containing specific domains of FHA will be used to screen human sera for specific antibody responses and potential correlates with protection will be investigated.